How do you know when your teeth bother you? The gums aren't red, it's …

How do you know when your teeth bother you? The gums aren't red, it's just been acting up for no reason, he's been fussy for three days now, it's hard to feed him all day, he keeps turning in different directions, I give him breast milk right away and he cries, I only feed him while he's sleeping, I see that he wants to eat. He has a full mouth of saliva since two months old. Relatives say his teeth are hurting, but where are they hurting if there's no swelling or redness.